The air/water syringe is a instrument commonly used by dentists for lavaging a patient's mouth to rinse away debris and for drying surfaces within the mouth during various dental procedures. During use, the tip of the syringe is inserted into a patient's mouth, and one or both selector valves on the hand piece of the syringe are activated to inject a stream of water and/or compressed air. When the operator releases the selector valve(s), fluid flow from the syringe tip is interrupted. However, fluid can flow back into the syringe from inside the mouth of the patient. This fluid is likely to carry microbes, which will be drawn into the passages at the tip of the syringe and further upstream, into the head and internal passages of the syringe. Even if the tip is replaced or sterilized between patients, the microbes within the syringe passages can infect patients who are subsequently treated. The problems can also arise in other types of dental instruments, such as high-speed hand pieces.
In recognition of this potential hazard, some manufacturers have installed check valves within the dental console or within the heads or handles of some models of dental instruments. Yet, such check valves, which are not intended to be replaced or maintained on a regular basis, can easily leak or fail completely; the failure is not evident and is difficult to detect. Even if a check valve is fully operational, capillary force developed in the small diameter lumens that extend through the dental instrument can cause aerosols or liquids from within the patient's mouth to be drawn back into the device. In certain syringe models, when the flow is interrupted by the selector valves, the movement of the valve creates a slight negative pressure pulse that can draw fluids back into the syringe tip. Turbulent fluid flow through a dental instrument can cause low pressure eddies that collapse once the flow is interrupted. Collapse of a low pressure eddy can create a negative pressure pulse that sucks fluid back into the internal passages of the instrument.
Although dentists commonly sterilize dental instruments and use disposable syringe tips and other components that are changed between patients, patients may not be protected against cross contamination caused by oral reflux. Fluid within the mouth of a patient who is undergoing dental surgery or even a simple cleaning often contains blood. If the blood and other fluids from within the patient's mouth are drawn into a syringe tip or inside the fluid passages of a hand piece, microbial contamination carried by the fluid can reach components of the instrument that are not sterilized or replaced between patients and the contaminants can be drawn back into the dental water lines. Subsequent patients, on which the instrument is used, are then exposed to the contamination carried by air/water from inside the instrument and the water lines, even if conveyed through an otherwise sterile tip. Moreover, patients subsequently treated may have water and/or air from the contaminated instrument or water lines injected into open wounds within their mouths.
The cross contamination problem can have serious medical consequences, particularly if the microbial contaminants include the HIV virus. Unfortunately, most dentists are unaware that the steps commonly taken to prevent cross contamination are inadequate to deal with oral reflux.
Another related problem arises from the contamination of air and water as these fluids flow through delivery lines from a dental console. The fluid lines that couple the dental console to the syringe or other dental instrument are subject to the growth of a biofilm on their inner surfaces; the biofilm serves as source of possibly pathogenic bacteria that contaminate the fluids flowing through the lines. A solution to this part of the problem is disclosed in commonly assigned U.S. Pat. No. 5,204,004 (Johnston et al.). In this prior patent, an in-line filter is installed in the water line conveying water to a dental syringe or other instrument, just upstream of the instrument. The downstream section of line is bacteriologically sterile. The filter includes a microporous membrane having a porosity selected to block a predefined size of particulate matter, including bacteria, without significantly restricting water flow. Bacteria released from any biofilm within the water line installed upstream of the filter are thus prevented from reaching a patient's mouth. However, the in-line filter cannot prevent oral reflux cross contamination when used without an operative check valve that is disposed in a position close to the dental instrument.
Clearly, it would be desirable to prevent cross contamination of dental patients due to oral reflux and to ensure that steps taken to prevent cross contamination by changing disposable syringe tips between patients are truly effective. Currently, there is no available solution to the problem or even a clear recognition that the problem is not adequately corrected by check valves built into the dental consoles or dental instruments.